Background/Purpose: Tumour necrosis factor alpha inhibitors are effective in reducing inflammation in rheumatic diseases while increasing the risk of infections. We aimed to study the relationship between trough serum concentrations of infliximab (CIFX) and the risk of a first infectious episode (IE) in treated patients.

Methods: We retrospectively included all patients who started infliximab treatment in our department. Patients were followed-up based on recommended infliximab infusions schedule. We studied the relationship between the occurrence of a first IE requiring hospitalization, anti-infectious treatment or infliximab infusion deferral, and the last CIFX and mean of 3 last CIFX (mean-CIFX) measured before the IE.

Results: From 201 patients retrieved, 173 spondyloarthritis patients with a mean age of 46 (±12) years and disease duration of 6.2 (±6.1) years were included in the analysis. During a median follow-up of 1.1 year, 87 patients had at least one IE. Using Cox models we found that the probability of survival without IE was significantly higher in patients with a mean-CIFX under the median (<11.3 mg/L) than in patients above the median (log-rang p=0.048). Glucocorticoid use and CIFX were significantly associated with the risk of a first IE in the multivariable analysis (p=0.004 for both). The risk of IE was significantly increased in the highest quartile of mean- CIFX (>20.3 mg/L, HR=2.65, 95%CI [1.14, 6.14], p=0.023; see figure 1)

Conclusion: We showed that a high infliximab concentration was correlated with a higher risk of a first infectious episode in spondyloarthritis. This finding needs to be replicated in further prospective studies.

Figure 1: Estimated Hazard Ratios (points) and 95% CI (vertical segments) for a first infectious episode in quartiles of the last 3 infliximab trough serum concentrations, adjusted for weight, CRP, ESR, disease activity, presence of ATI, methotrexate and glucocorticoid use.